System and Method for Manufacturing and Operating a Coaxial Tube Heat Exchanger

ABSTRACT

A coaxial heat exchanger is provided. Embodiments of the present disclosure relate to a coaxial heat exchanger for use in water source heat pumps or other applications involving fluid to fluid heat transfer. Embodiments of the present disclosure allow for the use of pre-existing engineered tubing with a textured or riffled interior surface and a folded fin intermediate member. Some methods of the present disclosure involve annealing and hydrostatically expanding the engineered tubing to increase contact and thermal transfer between the inner tube and the intermediate member. Additional systems, devices, and methods are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/984,525, filed Mar. 3, 2020. The entire disclosure of U.S.Provisional Application No. 62/984,525 is hereby incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to coaxial heat exchangers, and inparticular, to manufacturing processes and equipment for producingcoaxial heat exchangers, such as for HVAC systems and water source heatpumps.

BACKGROUND

This section is intended to introduce the reader to various aspects ofthe art that may be related to various aspects of the presentlydescribed embodiments—to help facilitate a better understanding ofvarious aspects of the present embodiments. Accordingly, it should beunderstood that these statements are to be read in this light, and notas admissions of prior art.

Modern residential and industrial customers expect indoor spaces to beclimate controlled. In general, heating, ventilation, andair-conditioning (“HVAC”) systems circulate an indoor space's air overlow-temperature (for cooling) or high-temperature (for heating) sources,thereby adjusting the indoor space's ambient air temperature. HVACsystems generate these low- and high-temperature sources by, among othertechniques, taking advantage of a well-known physical principle: a fluidtransitioning from gas to liquid releases heat, while a fluidtransitioning from liquid to gas absorbs heat.

In a typical system, a fluid refrigerant circulates through a closedloop of tubing that uses compressors and other flow-control devices tomanipulate the refrigerant's flow and pressure, causing the refrigerantto cycle between the liquid and gas phases. These phase transitionsgenerally occur within the HVAC's heat exchangers, which are part of theclosed loop and designed to transfer heat between the circulatingrefrigerant and outside environment. This is the foundation of therefrigeration cycle. The heat exchanger where the refrigeranttransitions from a gas to a liquid is called the “condenser,” and thecondensing refrigerant releases heat to the surrounding environment. Theheat exchanger where the refrigerant transitions from liquid to gas iscalled the “evaporator,” and the evaporating refrigerant absorbs heatfrom the surrounding environment.

A heat pump is a compression refrigeration system that is designed toreverse the flow of refrigerant to transition between heating andcooling modes. A reversing valve controls the direction of refrigerantflow through the refrigerant loop, thereby determining whether the heatpump is in heating mode or cooling mode. When the refrigerant flow isreversed, the potion of the refrigerant loop that previously functionedas an evaporator functions as a condenser and vice versa.

Water source heat pumps (WSHP) generally rely on two loops and one ormore heat exchangers that transfer heat between the loops. Water sourceheat pumps utilize a water loop and a refrigerant loop. Depending on themode of operation, heat is absorbed by one loop and transferred to theother. Heat is often transferred between the refrigeration loop andwater loop using coaxial heat exchangers.

Coaxial heat exchanges, also called tube-in-tube heat exchangers, areused in numerous applications including various heating, ventilation,air conditioning, and refrigeration (HVACR) applications. Like otherforms of heat exchangers, coaxial heat exchangers are used to transferheat from one fluid to another. While coaxial heat exchangers are alsoreferred to as tube-in-tube heat exchangers, neither the inner nor outertube is required to be round. Either the inner or outer tube may besubstantially any shape that allows a fluid to flow through the tube.The inner tube and outer tube are each designed to resist the workingpressures associated with the fluids within the inner and outer tuberespectively. In some coaxial heat exchangers, a tube may containgrooves, lobes, fins, projections, or other elements that increase thesurface area of a tube or promote a higher heat transfer coefficient,thereby allowing a greater exchange of heat between a fluid on theinterior of the tube and a fluid on the exterior of the tube.

In WSHPs, coaxial heat exchangers are used to transfer heat between therefrigerant within the refrigerant loop and the water, water/anti-freezesolution, or other fluid within the water loop. Water/anti-freezesolutions include, but are not limited to, water/methanol andwater/glycol solutions. The water or other fluid in the water loop thentransfers heat to the outside environment, such as the air or ground.

SUMMARY

Certain aspects of some embodiments disclosed herein are set forthbelow. It should be understood that these aspects are presented merelyto provide the reader with a brief summary of certain forms theinvention might take and that these aspects are not intended to limitthe scope of the invention. Indeed, the invention may encompass avariety of aspects that may not be set forth below.

Embodiments of the present disclosure generally relate to a heating,ventilation, air conditioning or refrigeration (HVACR) system adaptedutilizing a coaxial heat exchanger that has been formed according to thedisclosed methods. In some embodiments, engineered tubing may behydrostatically expanded to achieve a higher degree of contact and/or apress fit with an intermediate member. It will be appreciated thatexpanding the engineered tubing may create a friction fit and/orinterference fit with the intermediate sleeve. The engineered tubing andsleeve may be positioned within an outer jacket, thereby creating aninner fluid pathway and outer fluid pathway which may be used for fluidto fluid heat exchange.

Some embodiments of the present disclosure generally relate to a coaxialheat exchanger for water source heat pumps comprising an extrudedaluminum fin member comprising an interior and an exterior. In someembodiments, the interior of the extruded aluminum fin member has asubstantially circular interior diameter and the exterior of theextruded aluminum fin member comprises a plurality of projectingstructures. Some embodiments further comprise an engineered copper tubewith a rifled interior. In some embodiments, the engineered copper tubeis positioned within the extruded aluminum fin member and expanded usinghydrostatic pressure to increase contact between the exterior of theengineered copper tube and the interior of the aluminum fin member.Embodiments further comprise an outer jacket positioned outboard of theextruded aluminum fin member.

Some embodiments of the present disclosure generally relate to a methodfor manufacturing a coaxial heat exchanger, the method comprising thesteps of obtaining an engineered inner tube comprising an interior andan exterior, wherein the interior of the inner tube includes a rifledtexture; annealing the engineered inner tube; positioning the engineeredinner tube within the interior volume of an intermediate membercomprising an interior and an exterior wherein the exterior of theintermediate member comprises projecting structures; deforming theengineered inner tube using a pressure to increase contact between theexterior of the engineered inner tube and the interior of theintermediate member; and positioning the intermediate member andengineered inner tube within an outer jacketing member.

Various refinements of the features noted above may exist in relation tovarious aspects of the present embodiments. Further features may also beincorporated in these various aspects as well. These refinements andadditional features may exist individually or in any combination. Forinstance, various features discussed below in relation to one or more ofthe illustrated embodiments may be incorporated into any of theabove-described aspects of the present disclosure alone or in anycombination. Again, the brief summary presented above is intended onlyto familiarize the reader with certain aspects and contexts of someembodiments without limitation to the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of certain embodimentswill become better understood when the following detailed description isread with reference to the accompanying drawings in which likecharacters represent like parts throughout the drawings, wherein:

FIG. 1A illustrates schematically a heat pump in heating mode.

FIG. 1B illustrates schematically a heat pump in cooling mode.

FIG. 2 illustrates schematically a cross section of a coaxial heatexchanger according to one embodiment.

FIG. 3 illustrates schematically a coaxial heat exchanger according toone embodiment.

FIG. 4 illustrates schematically a portion of a coaxial heat exchangerutilizing projecting structures according to one embodiment.

FIG. 5 illustrates schematically a coaxial heat exchanger according toone embodiment.

FIG. 6 illustrates schematically a coaxial heat exchanger according toone embodiment.

FIG. 7 illustrates schematically a folded fin material according to oneembodiment.

FIG. 8 illustrates schematically a coaxial heat exchanger according toone embodiment.

FIG. 9 illustrates schematically a coaxial heat exchanger according toone embodiment.

FIG. 10 illustrates a data plot comparing the water side differentialpressure of two coaxial heat exchangers

FIG. 11 illustrates a data plot comparing the heat transfer of twocoaxial heat exchangers

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed. It should be appreciated that in the development of any suchactual implementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments, the articles “a,”“an,” “the,” and “said” are intended to mean that there are one or moreof the elements. The terms “comprising,” “including,” and “having” areintended to be inclusive and mean that there may be additional elementsother than the listed elements.

Turning to the figures, FIG. 1A and FIG. 1B each illustrateschematically a heat pump. A heat pump operates on the principal thatheat moves from a warmer material to a cooler material. A coil that iscooler than its surroundings will absorb head, and a coil that is warmerthat its surroundings will release heat.

FIG. 1A illustrates a heat pump 100 in heating mode. In heating mode,the outdoor heat exchanger 110 serves as an evaporator and absorbs heatfrom its surroundings. Conversely, the indoor heat exchanger 120 servesas a condenser and releases heat to its surroundings. Low-pressureliquid refrigerant or a liquid-vapor mixture enters the outdoor heatexchanger 110, absorbs heat from the surrounding environment, andvaporizes. The low-pressure refrigerant vapor then enters the compressor130 where it is compressed to a high-temperature and high-pressurevapor. The high-temperature, high-pressure vapor then enters the indoorheat exchanger 120 where it releases heat to the surrounding environmentand condenses to a high-pressure liquid. The high-pressure liquid passesthrough a metering device 140, such as thermal expansion valve or acapillary tube, where it becomes a low-pressure liquid or liquid-vapormixture and enters the outdoor heat exchanger and then repeats theprocess. It will be appreciated that the “indoor” heat exchanger is notrequired to be physically indoors. In certain HVAC applications, theindoor heat exchanger may be in communication with the indoor air, awater loop, or another system that communicates heat, directly orindirectly, to the area to be climate controlled. It will similarly beappreciated that the “outdoor” heat exchanger is not required to bephysically outdoors. In certain HVAC applications, the outdoor heatexchanger may be in communication with a water loop or other system thatcommunicates heat, directly or indirectly, to the outside environment.

FIG. 1B illustrates a heat pump 101 in cooling mode. In cooling mode,the heat pump operates on the same underlying principal, but the outdoorheat exchanger 111 serves as a condenser and releases heat to itssurroundings. Conversely, the indoor heat exchanger 121 serves as anevaporator and absorbs heat from its surroundings. The flow ofrefrigerant may be reversed when the reversing valve 151 changesposition.

In water source heat pumps (WSHPs) the refrigerant transfers heat toand/or from a flowing stream of water or water-antifreeze mixture. Thistransfer of heat is typically performed using a coaxial heat exchanger.The water to refrigerant heat exchanger is generally referred to as theoutdoor heat exchanger although it will be appreciated that the outdoorheat exchanger may be positioned indoors.

FIG. 2 schematically illustrates a cross section of coaxial heatexchanger 200 according to one embodiment. The inner tube 210 of theheat exchanger 200 is configured to allow water to flow through theinner tube. In some embodiments, the interior surface of the inner tube210 is rifled, knurled, patterned, or otherwise textured in order toincrease the heat transfer between water flowing through the inner tubeand the material of the inner tube itself. In some embodiments, theinner tube 210 is engineered tubing or tech tube. In some embodiments,the inner tube 210 comprises copper, copper-nickel allow, titanium,and/or stainless steel. In some embodiments, the inner tube is anevaporator tube such as, for example, B4 or B5 tubes. In someembodiments, the inner tube is a condenser tube such as, for example,C+LW or C5 tubes.

Coaxial heat exchanger 200 also includes an intermediate member 220positioned outboard of the inner tube 210. The intermediate member 220may be a configured as a sleeve with projecting members, folded fins, ora combination of the two. In some embodiments, a folded fin intermediatemember may be arranged as a ruffled folded fin, plain folded fin, and/ora lanced and offset folded fin. In some embodiments, the projectingstructures and/or fins of the intermediate tubing member may betextured, twisted, and/or axially rifled. In some embodiments, thesesurface features increase the mixing and/or turbulence of a flowingfluid, thereby enhancing the degree of heat transferred between theintermediate tubing member and the fluid.

As shown in FIG. 2, when intermediate member 220 is configured as afolded fin, portions of the folded fin are in contact with the innertube 210, thereby allowing heat transfer from the inner tube 210 to theintermediate member 220. The increased surface area created byintermediate member allows for increased heat transfer.

In some embodiments, intermediate member 220 is initially in a generallyplanar configuration and is wrapped around the inner tube 210 to form atubular intermediate member. In some embodiments, the intermediatemember is brazed to itself to maintain a tubular configuration ratherthan a planar form. Depending on the respective length of the inner tubeand the intermediate member, in some embodiments, multiple intermediatemembers sections may be wrapped around the inner tube or positionedaxially around the inner tube. In some embodiments, an intermediatemember section is between 4 to 6 inches long. In some embodiments, anintermediate member 220 may comprise one or more than one intermediatemember sections. In some embodiments, the intermediate member sectionsmay be in contact with each other. In some embodiments, the intermediatemember sections are separated by a gap. In some embodiments, the gapbetween intermediate member sections is smaller at the first or lastportion of the heat exchanger as compared to the middle portion of theheat exchanger. In some embodiments, an intermediate member comprises aplurality of rings axially aligned around the inner tube. In suchembodiments, one or more than one of the rings includes axiallyprojecting structures.

The intermediate member 220 is positioned within an outer jacket 230.The outer jacket 230 is outboard of the intermediate member 220 and theinner tube 210. In some embodiments, the outer jacket 230 is rigid. Insome embodiments, the outer jacket 230 contains metal, such as, forexample, steel, stainless steel, copper, or aluminum. The outer jacket230 is sufficiently strong to resist deformation at the appropriateworking pressures such as, for example, refrigerant pressures.

The volume contained within the interior of the inner tube 210 isreferred to as the inner volume 240. The volume between the interior ofthe outer jacket 230 and the exterior of the inner tube 210 is referredto as the outer volume 250.

In some embodiments, the coaxial heat exchanger 200 allows a first fluidto flow through the inner volume 240 while a second fluid flows throughthe outer volume 250. Heat is exchanged between the first and secondfluids through the inner tube 210 and the intermediate member 220. Insome embodiments, the first fluid is water and the second fluid is arefrigerant which undergoes a phase change as heat is exchanged betweenthe water and refrigerant.

In some embodiments, in order to create and/or increase contact betweenthe inner tube 210 and the intermediate member 220, the inner tube isexpanded or otherwise deformed. The inner tube 210 may be expanded usingpressure, such as, for example, hydrostatic pressure, or usingmechanical expansion processing. In some embodiments, it is advantageousto expand the inner tube 210 using hydrostatic pressure in order toavoid crushing or significantly deforming the texture and/or rifling onthe interior surface of the inner tube 210.

In some embodiments, before the inner tube 210 is expanded, the innertube 210 is annealed. The inner tube 210 is annealed by heating it to apredetermined temperature and allowing the inner tube 210 to cool at acontrolled rate. Once the inner tube 210 is annealed, the inner tubematerial is generally softer and may be more easily expanded.

In some embodiments, the inner tube 210 is optimized to transfer heatbetween a water solution in the inner volume 240 and a refrigerant inthe outer volume 250 when the refrigerant is in a two-phase mixture oris in the process of changing phases (either evaporation orcondensation). In some embodiments, the exterior of the inner tubecontains ridges that are optimized to promote the evaporation ofrefrigerant by facilitating the formation of bubbles when therefrigerant evaporates. In some embodiments, the exterior of the innertube contains ridges that are optimized to promote the condensation ofrefrigerant by facilitating the formation of droplets when therefrigerant condenses. It will be appreciated that embodiments that areoptimized to facilitate evaporation of the refrigerant will also promotecondensation of the refrigerant when compared to an inner tube with agenerally smooth exterior surface.

In some embodiments, the first and/or last portions of a condenser orevaporator generally contain more single-phase refrigerant while themiddle portion contains more liquid-vapor mixture. Accordingly, in someembodiments, engineered tubing with an enhanced textured exteriorsurface may be used for the middle portion of the inner tube and tubingwith a smooth or otherwise unenhanced exterior surface may be used forthe first and/or last portion of the inner tube. In some embodiments,regardless of the state of the exterior surface of the inner tube, theinterior surface of the inner tube will contain an engineered texturedsurface to take advantage of the increased turbulence and heat transferwith the liquid water solution flowing through the interior of the innertube.

In some embodiments, the intermediate member increases the surface areain contact with a refrigerant, whether the refrigerant is in asingle-phase (liquid or vapor) or in a two-phase mixture. In someembodiments, the intermediate member facilitates greater heat transferwhen the refrigerant is in a single phrase as compared to when therefrigerant is in a two-phase mixture. In some embodiments, theintermediate member is only present at the first and last portions ofthe coaxial heat exchanger. In some embodiments, the intermediate memberis not included in the portions of the heat exchanger that are expectedto contain significantly two-phase mixtures of refrigerant. In someembodiments, the intermediate member is made of multiple intermediatemember sections. In some embodiments, there is a gap between eachintermediate member section. In some embodiments, the gap betweenintermediate member sections is larger in the middle portion of thecoaxial heat exchanger as compared to the end portions of the heatexchanger. In some embodiments, the gap between intermediate membersections is larger in the four feet middle section of a ten feet longheat exchanger than in the three feet sections at either end of the tenfeet long heat exchanger.

In some embodiments, the linear length of a coaxial heat exchanger isabout ten feet. In some embodiments, about three-foot long sectionsclosest to the ends of the heat exchanger contain inner tube memberswith a generally smooth or otherwise unenhanced exterior surface whilethe middle about four-foot section contains enhanced engineered innertube with an exterior surface designed to promote evaporation orcondensation of the refrigerant.

FIG. 3 schematically illustrates a coaxial heat exchanger 300 accordingto one embodiment. Heat exchanger 300 includes a copper inner tube 310,an intermediate member 320 configured in a folded fin design, and asteel outer jacket 330. FIG. 3 also illustrates fluid inlet 340 thatallows a second fluid to flow into the outer volume 360 to exchange heatwith a first fluid in the inner volume 350. Not shown in FIG. 3 is ananalogous fluid outlet that allows the second fluid to exit the outervolume of the coaxial heat exchanger 300.

FIG. 4 schematically illustrates a coaxial heat exchanger 400 accordingto one embodiment. FIG. 4 illustrates an inner tube 410 and anintermediate member 420. For clarity, FIG. 4 does not show an outerjacket. In some embodiments, inner tube 400 comprises copper and has atextured or rifled interior surface. In some embodiments, the outersurface of inner tube 410 is generally smooth. In some embodiments,intermediate member 420 comprises extruded aluminum such as, forexample, a single piece of extruded aluminum. Aluminum may be extrudedto form particular cross-sectional designs. As shown in FIG. 4,intermediate member 420 may include a generally circular interiorsurface 423 with projecting structures 425 radiating therefrom. Thegenerally circular interior surface 423 of intermediate tubing member420 allows for a high degree of contact between the intermediate member420 and the inner tube 410.

In some embodiments, contact between the inner tube 410 and theintermediate tubing member 420 is increased by annealing the inner tube,then axially inserting the annealed inner tube into the intermediatetubing member and hydrostatically expanding the annealed inner tubewithin the intermediate tubing member. This process creates an increaseddegree of contact and facilitates heat transfer between the inner tube410 and the intermediate tubing member 420. This arrangement allows theintermediate tubing member 420 to transfer heat between the first fluid,flowing within the inner volume within the inner tube 410 to or from asecond fluid flowing in the outer volume between the intermediate tubingmember 420 and the outer jacket (not shown) without the intermediatetubing member 420 being in contact with the first fluid. In someembodiments, the first fluid contains water and the second fluidcontains a refrigerant such as, for example, R410A, R32, R454B, DR-55,R134a, R513A, R515A, R515B, HFO refrigerants such as HFO-1234ze,HFO-1233zd, or HFO-1234yf, or any number of combinations thereof.Expanding the annealed inner tube within the intermediate tubing memberincreases contact between the inner tube and intermediate member therebyfacilitating thermal transfer. In some embodiments, expanding the innertube within the intermediate member creates a press fit. Thisarrangement prevents the material of the intermediate tubing member fromcontacting the first fluid within the inner tube. This arrangementallows the intermediate member to contain materials that may not besuitable for sustained contact with the first fluid. Expanding theannealed inner tube using hydrostatic pressure allows the use ofpre-existing engineered tubing or tech tube that has a rifled interiorsurface to be used with an extruded aluminum intermediate tubing member.

FIG. 5 schematically illustrates a coaxial heat exchanger 500 accordingto one embodiment. FIG. 5 illustrates an inner tube 510 and anintermediate member 520. Intermediate member 520 is an extruded member.In some embodiments, the extruded tube member 520 includes a generallycircular inner surface 523 and a generally circular outer surface 525with a plurality of channels 527 passing through the length of the tubemember 520. This arrangement allows the tube member to form a highdegree of contact and thermal transfer between the tube member and theinner tube, thereby facilitating a high degree of thermal transferbetween the first fluid flowing through the inner tube and the secondfluid flowing through the channels 527 of the tube member 520. In someembodiments, the outer surface 525 of the tube member 520 is connectedto a coupling 550. Fluid inlet 540 allows fluid to enter the volumebetween the coupling 550 and the inner tube 510. This volume is in fluidcommunication with the channels 527 that pass through the tube member520. The tube member 520 is positioned axially outboard of the innertube 510. A coupling 550 seals the outer volume, causing the secondfluid to flow through the fluid inlet/outlet 540 in order to passthrough the outer volume. In some embodiments, no separate outer jacketis required as the second fluid is contained within the volume definedby the channels of the extruded tube member and the coupling 550.

In some embodiments, the coupling 550 is also in contact with theexterior surface of the inner tube 510. In some embodiments, thecoupling is sealed, adhered, and/or brazed to the exterior surface ofthe inner tube 510 and exterior surface of the tube member 520 toprevent leakage of the second fluid. In such embodiments, no outerjacket is required.

FIG. 6 schematically illustrates a coaxial heat exchanger 600 accordingto one embodiment. In some embodiments, the intermediate member 620includes a fin portion 623 and a non-fin portion 625. In someembodiments, the intermediate member is formed as an aluminum extrusionwith fins or other projecting structures along the length of theintermediate member. In some embodiments, the fins or projectingstructures are machined off or otherwise removed from the intermediatemember, thereby forming the non-fin portion of the intermediate member.

In some embodiments, the intermediate member serves as a double wallconstruction around the inner tube 610. This double wall constructionprevents any mixing of the first and second fluids in the event thateither the inner tube 610 or the intermediate member 620 corrodes orotherwise becomes damaged, resulting in a leak. In some embodiments, theouter jacket 630 is sealed around the non-fin portion 625 of theintermediate member 620. In some embodiments, the outer jacket 630 isarranged so that no separate coupling is required. As shown in FIG. 6,in some embodiments, the fluid inlet/outlet may be incorporated into theouter jacket 630, allowing fluid to flow into or out of the outer volumebetween the outer jacket 630 and the intermediate member 620.

In some embodiments, the outer jacket 630 is brazed to the intermediatemember 620 and any space between the intermediate member and inner tubeis left open to the atmosphere. In such embodiments, if the intermediatemember becomes damaged, any refrigerant flowing through the outer zoneis released into the atmosphere rather than contaminating thecirculating water solution within the inner tube. It will be appreciatedthat any space between the inner tube and intermediate member is verysmall and does not significantly reduce the thermal transfer between thefirst and second fluids.

FIG. 7 illustrates a folded fin structure 700 in a planar or flat formaccording to one embodiment. In some embodiments of the heat exchanger,the folded fin structure 700 is wrapped, rolled, or otherwise positionedaround an inner tube to form the intermediate member.

FIG. 8 illustrates a heat exchanger 800 according to one embodiment. Itwill be appreciated that the components of heat exchanger 800 have beenpositioned for clarity. Engineered inner tube 810 includes a texturedinterior surface and a textured exterior surface. Intermediate member820 is configured as a folded fin. Intermediate member 820 is positionedaxially outboard of the engineered inner tube 810. In some embodiments,intermediate member 820 is initially a substantially flat or planarmember and is wrapped around inner tube 810. The innertube 810 andintermediate member 820 are positioned within outer jacket 830.

In some embodiments, the intermediate member is configured to create anaxial gap portion 840. The exterior surface of the inner tube isgenerally not covered by the intermediate member in the axial gapportion. In some embodiments, the heat exchanger is coiled after it isassembled. In some embodiments, the axial gap portion allows the heatexchanger to be coiled while reducing the amount of crimping or crushingof the intermediate member. If the intermediate member weresignificantly crimped or crushed, the damaged portion of theintermediate member could restrict the flow of fluid through the volumebetween the inner tube and outer jacket. In some embodiments, the axialgap portion is positioned at the interior radius of the coiled coaxialheat exchanger.

In some embodiments, a spacer (not shown) may be positioned axially tothe inner tube. In some embodiments, the spacer may be positioned in theaxial gap portion. In some embodiments, the spacer comprises a flexiblematerial that allows fluid to pass through the spacer such as, forexample, copper wool.

FIG. 9 illustrates a heat exchanger 900 according to one embodiment. Theinner tube 910 includes a rifled interior surface and a texturedexterior surface. Intermediate member 920 is in contact with both theinner tube 910 and the outer jacket 930. In some embodiments, inner tube910 has been hydrostatically expanded in order to increase contactbetween the inner tube 910 and the intermediate member 920 withoutdeforming the texture on either the interior or exterior surfaces of theinner tube 910. In some embodiments, the outer jacket 930 orintermediate member 920 may be shrunk once the inner tube 910 ispositioned within the outer jacket 930 or intermediate member 920 inorder to create a press fit or otherwise increase contact between theintermediate member 920 and the inner tube 910.

FIG. 10 illustrates a data plot comparing the water side pressure dropof an example embodiment of the coaxial heat exchanger described herein(square data points) and a commercially available fluted tube coaxialheat exchanger (diamond data points). When water is pumped into acoaxial heat exchanger the water enters the heat exchanger at a higherpressure than the water exits the heat exchanger. This drop in pressureis due to liquid friction and turbulence created within the heatexchanger. The greater the drop in pressure, the more energy must beused to pump water into the heat exchanger.

As shown in FIG. 10, the coaxial heat exchanger according to oneembodiment described herein had a lower water side pressure drop thanthe commercially available fluted tube heat exchanger at all flow rates.The difference in waterside pressure drop increases as the flow rateincreases.

FIG. 11 illustrates a data plot comparing the heat transfer of anexample embodiment of the coaxial heat exchanger described herein(square data points) and a commercially available fluted tube coaxialheat exchanger (diamond data points). As can be seen in FIG. 11, thecoaxial heat exchanger according to one embodiment described herein hada greater heat transfer than the commercially available fluted tube heatexchanger at all flow rates. The difference in heat transfer increasesas the flow rate increases.

While the aspects of the present disclosure may be susceptible tovarious modifications and alternative forms, specific embodiments havebeen shown by way of example in the drawings and have been described indetail herein. But it should be understood that the invention is notintended to be limited to the particular forms disclosed. Rather, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by thefollowing appended claims.

1. A coaxial heat exchanger for water source heat pumps comprising: aninner tube, wherein the inner tube has a textured interior surface and atextured exterior surface; an intermediate member positioned outboard ofthe inner tube; and an outer jacket comprising an interior and exterior,wherein the outer jacket is positioned outboard of the intermediatemember.
 2. The coaxial heat exchanger of claim 1, wherein the inner tubecomprises copper or a copper bearing alloy.
 3. The coaxial heatexchanger of claim 1, wherein the exterior surface of the inner tube isconfigured to increase heat transfer to a condensing or evaporatingfluid and the interior surface of the inner tube is configured toincrease heat transfer to a single-phase fluid.
 4. The coaxial heatexchanger of claim 1, wherein the intermediate member comprises a foldedfin.
 5. The coaxial heat exchanger of claim 1, wherein the outer jacketcomprises steel and is brazed to the inner tube.
 6. The coaxial heatexchanger of claim 1, wherein the intermediate member is configured tocreate an axial gap portion, wherein the exterior surface of the innertube is not covered by the intermediate member in the axial gap portion.7. The coaxial heat exchanger of claim 6, further comprising a spacerpositioned axially parallel to the inner tube in the volume between theinner tube and the outer jacket.
 8. The coaxial heat exchanger of claim1, wherein the intermediate member comprises more than one intermediatemember section.
 9. The coaxial heat exchanger of claim 1, wherein theinner tube is annealed and hydrostatically expanded within theintermediate member.
 10. The coaxial heat exchanger of claim 1, whereinthe heat exchanger is coiled and has about a ten-inch diameter.
 11. Amethod for manufacturing a coaxial heat exchanger, the methodcomprising: obtaining an engineered inner tube comprising an interiorsurface and an exterior surface, wherein the interior surface andexterior surface of the engineered inner tube are textured; positioningan intermediate member comprising an interior and an exterior axiallyoutboard of the engineer inner tube; positioning the intermediate memberand engineered inner tube within an outer jacket; and deforming at leastone of the engineered inner tube, intermediate member, or outer jacketto increase thermal transfer between the engineered inner tube and theintermediate member.
 12. The method of claim 11, further comprisingannealing the engineered inner tube.
 13. The method of claim 11, whereinthe deforming comprises expanding the engineered inner tube usinghydrostatic pressure.
 14. The method of claim 11, wherein the deformingcomprises shrinking the intermediate member or outer jacket.
 15. Themethod of claim 11, wherein the interior surface of the engineered innertube is rifled.
 16. The method of claim 11, wherein the engineered innertube comprises copper or copper bearing alloy.
 17. The method of claim11, wherein the intermediate member comprises extruded aluminum.
 18. Themethod of claim 11, wherein the intermediate member comprises a foldedfin.
 19. The method of claim 11, further comprising brazing the outerjacket to the intermediate member.
 20. A water source heat pumpcomprising: a compressor in fluid communication with a refrigerant line;a reversing valve configured to adjust the direction of refrigerantflowing in at least a portion of the refrigerant line; a water linewherein the water line is in thermal communication with the outsideenvironment; and a coaxial heat exchanger comprising: an inner tube influid communication with the water line, wherein the inner tube has atextured interior and exterior surface; an intermediate memberpositioned outboard of the inner tube wherein the intermediate memberhas a folded fin structure; and an outer jacket positioned outboard ofthe intermediate member to define a volume between intermediate memberand the outer jacket, the volume being in fluid communication with therefrigerant line.